1. Field of the Invention
The present invention relates, generally, to compression spray applicators for coating fluids, and more particularly such a spray applicator for spraying viscous fluids, such as plaster or other texturizing materials onto a wall, ceiling or the like.
2. Background Art
One problem in such applicators, and particularly when dealing with the application of plaster or similar materials, is that when the spray operation first begins, and oftentimes at its termination, there is the problem of the material "dribbling" during the startup, and also at the time when the fluid flow is terminated. One means of solving this is to have the discharge stem positioned against the discharge opening through which the plaster or other material is sprayed. The pressurized air is first caused to move through a central passageway in the discharge stem and out the forward exit end thereof, after which the stem is moved rearwardly from the discharge opening to permit the plaster or the like to flow into the air jet to be sprayed from the discharge opening. Also, upon termination of the particular spray application, the discharge stem is caused to again seal against the discharge opening while air is still being discharged through the stem, so as to prevent the dribbling at the end of the operation.
There are various examples in the prior art showing this general mode of operation. For example, U.S. Pat. No. 1,609,465 shows a paint sprayer where the paint is supplied to a spray gun through a first passageway and pressurized air through another. When an operating trigger is depressed, the portion of the pressurized air activates a diaphragm which is moved rearwardly against the force of a biasing spring which would normally maintain a valve member in a closed position. As the valve member moves rearwardly, it opens the spray nozzle so paint can flow from the reservoir into the air stream. Thus, there is an issuance of the propelling air through the nozzle for a very short time period immediately prior to the movement of the diaphragm and likewise causes the air to flow for a slight time period after the force of the diaphragm is released, to ensure that all the paint is atomized, and thus prevent unwanted spattering.
A similar approach is shown in U.S. Pat. No. 1,332,554. This also shows a spray gun used for depositing paints or other coatings. Air is admitted through one passageway and the paint or other fluid via another passageway. The stem through which the air is discharged is initially sealed against the discharge port of a chamber containing the paint or other material. When pressurized air is delivered into the device, the stem is retracted by action of the air pressure against a biasing string so that the paint may be propelled by the air stream through the port. Both this patent and the patent mentioned immediately above have a handle which can be grasped in the hand, as well as an operating trigger.
U.S. Pat. No. 4,411,387 shows a manually operated spray applicator, one of the co-inventors in that patent, Donald J. Stern, being the inventor in the present application. This shows a spray applicator where there a manually operated piston to supply the pressurized air. The piston is moved forwardly to pressurize a rear main pressure chamber to cause air to flow through a discharge stem that is seated so as to close a discharge port for the plaster or the material. There is a bypass passageway leading from the main pressure chamber to a secondary pressure chamber where there is a control piston that is fixably connected to the discharge stem. As air flows through this bypass passageway, it pressurizes the second pressure chamber to move the stem rearwardly away from its seat, against the urging of a biasing spring, so as to permit the plaster or the material to flow into the region of the port, with the air jet causing this to be discharged in the form of a spray. When the manually operated pressure piston passes a certain location in the main pressure chamber, the bypassed passageway is exposed to ambient air to release pressure in the secondary pressure chamber and cause the discharge stem to move to its forward position to close the discharge port.